Medial epicondyle morphology and medial elbow gapping in high school baseball players: implications for...

In adolescent baseball players, repetitive valgus stress during throwing leads to morphological adaptations of the medial epicondyle. Medial elbow gapping (Gap) is used to assess medial elbow laxity. However, the relationships among medial epicondylar morphology, Gap, and throwing-related elbow pain remain unclear. We hypothesized that players with medial epicondyle protrusion would demonstrate increased Gap and that Gap measured under valgus stress (Gap-stress) would show a stronger association with throwing-related elbow pain than Gap measured at rest, particularly among those with recent pain.

Ninety-five high school baseball players competing at a national tournament level were included. Medial epicondyle morphology (protrusion, fragmentation, and irregularity) and Gap were assessed using ultrasonography. Gap was measured at rest (Gap-rest) and under valgus stress (Gap-stress), and the difference between these measurements was calculated as ΔGap. Based on temporal characteristics, throwing-related medial elbow pain was classified into 3 categories: current elbow pain, elbow pain within the past year, and history of elbow pain. Associations between medial epicondyle morphology and Gap were examined using group comparisons, whereas associations between Gap and pain outcomes were evaluated using logistic regression.

Gap-rest, Gap-stress, and ΔGap were 3.3 ± 0.8 mm, 3.9 ± 1.1 mm, and 0.6 ± 0.8 mm, respectively. Current elbow pain was present in 8 players (8.4%), elbow pain within the past year in 20 players (21.1%), and a history of elbow pain in 61 players (64.2%). After Bonferroni correction, no medial epicondyle morphology-Gap comparison remained statistically significant. Among the position-adjusted Gap-pain models, only Gap-stress remained significantly associated with elbow pain within the past year (odds ratio, 2.36; 95% confidence interva, 1.38-4.05; adjusted P = .016). Gap-rest and ΔGap were not significant after correction, and no Gap parameter was associated with current pain or more remote pain history. No significant interaction was observed between medial epicondyle protrusion and any Gap parameter for past-year elbow pain.

Medial epicondyle morphology was not associated with increased Gap in high school baseball players. Gap-stress was significantly associated with elbow pain within the past year, whereas Gap-rest and ΔGap were not significant after correction for multiple comparisons. These exploratory findings suggest that, rather than being a static structural characteristic, Gap-stress may reflect a dynamic mechanical state of the medial elbow associated with relatively recent pain.